1. Field of the Invention
This invention relates to fluid purification systems and more particularly to fluid purification systems incorporating fluid exposure to both ultraviolet radiation and filtration.
2. Description of the Prior Art
In an attempt to provide high quality, potable drinking water, various treatment systems have been developed. Many such systems employ activated carbon filters, as a common treatment to remove odor, improve taste, and remove chemicals, such as chlorine and chloroforms. However, carbon is a nutrient source that supports bacteria life and growth. As a result, unless these filters are replaced frequently, the filters themselves provide a breeding ground for bacterial contamination. This bacteria is spread to the consumer as the water flows through the filter, picking up the bacterial contamination and delivering the bacteria to the user.
It has been found that activated charcoal filters are so conducive to bacterial growth that filters not routinely replaced may provide more bacterial contamination to the water than the unfiltered water itself. In addition, the bacteria tend to occupy many of the absorptive sites in the filter, reducing the filter's absorptive capacity and rendering the filter ineffective for its intended purpose of purifying the water.
It is well known that exposure of water to ultraviolet radiation kills microorganisms and bacteria carried by the water. For this reason, many conventional purification systems employ an ultraviolet sterilization unit in series with a filtration unit.
Many attempts have been made to use ultraviolet (UV) sterilization in conjunction with a reverse osmosis (RO) water treatment system. The results obtained in these attempts, however, have been less than satisfactory. Additionally, these combined UV and RO systems have been bulky and impractical for many uses, particularly consumer applications. Another significant barrier to many applications is the high cost of such systems, a major contributor to the cost being the expensive ultraviolet sterilizer.
Reverse osmosis water treatment systems were primarily developed as a technique to remove many of the toxic chemicals, dissolved solids and other contaminants in water. They were also developed for use in the desalination process to convert sea water into usable water. While many manufacturers have claimed that the systems are also capable of removing bacteria and other microbiological contents, the problems faced by a reverse osmosis system in doing this are substantially equivalent to those faced in the high purity water field, that is, the unit attempts to filter the bacteria out as opposed to destroying them.
The reverse osmosis process relies on the ability to permeate water under pressure through a small pore size porous membrane that blocks the flow of the contaminants allowing only the purified water through. The process has been applied successfully in the removal of most contaminants except bacteria and other microorganisms. This fact is recognized by the RO industry as exemplified by their attempts to use ultraviolet sterilization in conjunction with their units. Bacteria can, and do, collect on the membrane surface causing a "sliming" or "fouling" condition that impedes the efficiency and performance of the system. In addition, the bacteria can, and do, penetrate the membrane exiting the system in the "purified water".
The operation of a reverse osmosis system also relies on the fact that only a small amount of the water flowing through the system is "purified". The rest of the water exits the system through a discharge line carrying the contaminants to waste. For this reason, a typical reverse osmosis unit can not provide sufficient water for use "on demand". Consequently, most systems have a storage tank to collect the "purified" water for later use. FIG. 17 is a block diagram of a typical prior art reverse osmosis unit showing the inlet, outlet and discharge ports. FIG. 19 is a block diagram of a typical prior art reverse osmosis system, incorporating a carbon filter and a storage tank. This system is common to units intended for providing "purified" water for consumption.
With reference to FIG. 17, source water enters the reverse osmosis unit 60 through the inlet port 61. The water then passes by the membrane where a portion of the water permeates through the membrane and exits the unit via the outlet port 62. The other portion of the water exits the unit via the discharge port 63. In this system there are three prime sources of microbiological contamination, the source water, the discharge line and the exit point for the "purified" water or "point of use".
With reference to FIG. 19, source water enters the reverse osmosis unit 60 through the inlet port 61, passes by the membrane where a portion permeates through the membrane, exits the RO unit into a carbon filter 64 which serves as a "polisher" and into a storage tank 66. The other portion of the water flows through the discharge port 63 to waste. In this system, the microbiological contamination sources are substantially greater. In addition to the three sources previously mentioned, the carbon filter represents a fertile "breeding ground" to support microbiological growth and the storage tank rapidly becomes loaded with microorganisms. It is not uncommon to find orders of magnitude greater numbers of organisms exiting this system than present in the source water.
An example of an attempt to use UV in conjunction with an RO system is shown in the Veloz patent, U.S. Pat. No. 3,550,782. In this application, Veloz recognized the need for protection of the RO unit from microbiological contamination but drew incorrect conclusions as to the proper application of the ultraviolet sterilization. In the disclosure of this patent, Veloz ignored, and does not even show, the discharge line coming from the RO unit. Since this line connects directly to a waste line in most systems, it represents a significant source of microbiological contamination. Additionally, the storage tank is shown outside the ultraviolet protection thus allowing organisms to enter and grow within the tank. While the microbiological contamination problems encountered in this design might be overcome by continual teardown and sterilization of the components, it is both expensive and impractical for most applications, particularly in a consumer application. This represents a significant health hazard to the unsuspecting or unknowledgeable user.
Attempts have also been made to use ultraviolet sterilization in conjunction with a deionization (DI) water treatment system. The results obtained in these attempts, however, have also been less than satisfactory. These combined UV and DI systems have been bulky and impractical for many uses. Conventional ultraviolet sterilizers require continuous maintenance to keep them operating efficiently. This, along with the high cost of such system, the ultraviolet sterilizer being a major contributor to the cost, make them impractical for many applications.
Deionization systems were designed to remove waterborne contaminants, primarily those which contribute to the "fouling process" in a fluid conduit or fluid system. Typical examples of DI system applications are water softeners and water treatment units to provide feed water for distillation or other equipment. In both of these cases, the units are intended to prevent the build up of scale deposits on pipe or equipment surfaces.
Deionization systems were not designed with regard to the potential microbiological contaminations problems associated with the use of the systems. As state of the art advancements in technology occurs, the use of deionization systems for producing high quality water for sophisticated instruments has increased substantially. These applications have placed higher demands on the efficiency and performance factors of deionizers. In many areas, the systems are utilized with the intent to produce either organically pure or microbiologically pure water.
Referring to FIG. 22, generally shown is a prior art deionizer consisting of a cation, anion or combination cation/anion resin bed. Source water flows through the resin bed(s) where an ion exchange process takes place, the unwanted ions being deposited on the exchange sites and the "harmless" ions being transferred into the water. The materials used in the deionizer beds are supportive to microbiological life and growth. Consequently these beds become contaminated with microorganisms creating a "slimy" coating on the resins that interferes with the system performance by "blocking" the exchange sites.
FIG. 24 is a block diagram of a prior art typical deionization system which consists of a carbon filter and two resin beds. In this configuration, the initial resin bed is sometimes referred to as the roughing bed, the second sometimes referred to as the polishing bed. In this system, the addition of a carbon filter will enhance the growth of microorganisms, speeding up the process of contamination throughout the DI system.
FIG. 26 is a block diagram of a prior art deionization system used in high purity water applications. In this system, a recirculation loop is added to provide greater efficiency of operation. There is some thinking that keeping the water moving through the system, particularly when the system is not in use, will tend to reduce the microbiological build up.
In all of the above cases, the deionization system is constantly being supplied with new microorganisms from the source water and from the "point of use" allowing growth to occur within the system. Consequently, from the time a system is initially set up, microbiological growth is increasing until the point is reached where the system is "overloaded". At this point, the carbon and resin beds must be replaced.